The most audacious building project among many initiated by the Roman emperor Publius Aelius Hadrianus (known as Hadrian) was the defensive rampart across the entire width of Britain that marked the northern frontier of the Roman Empire for almost 300 years. Started in a.d. 123 Hadrian’s Wall was about 73 miles (118 kilometers) long, stretching from what is now the town of Wallsend (Roman Segedunum) on the River Tyne in the east to modern Bowness (Roman Banna) on the Solway Firth in the west. From there, seaward defenses, somewhat less substantial, turned south along the Cumberland coast for another 40 miles (65 kilometers).
Spurred by his conquest of Gaul, Julius Caesar undertook a reconnaissance of Britain in 55 b.c. A full-scale Roman invasion took place in a.d. 43, when Claudius was emperor, and there followed decades of resistance by various local tribes. But Britain, soon known as “the food basket of Rome,” was too rich a prize to surrender. Under the governor Petilius Cerealis, the legions marched north into the territory of the Brigantes and established a base at York (Roman Eboracum) in a.d. 71. About ten years later, they pushed forward into Scotland, creating a temporary frontier between the Rivers Forth and Clyde. They intended to consolidate their new conquests by constructing roads and forts (caestra), but the northern tribes proved too warlike, causing the Romans to strategically withdraw.
Hadrian, the adopted son of Trajan, reigned from a.d. 117 until 138. He loved to build: among his architectural schemes in and near Rome were his own tomb (later known as the Castel Sant’ Angelo), the Pantheon, and a luxurious country villa at Tivoli. He was also an inveterate traveler and for over half of his reign he was away from Rome, mostly touring the eastern provinces and North Africa. On a visit to Britain in 122 he appointed a new governor, Aulus Pletorius Nepos, and in order to establish a presence in the far north, he commissioned the construction of the Wall to “separate the Romans from the barbarians.” Work started the following year. As planned, the eastern sector between Wallsend and the River Irthing was to be a stone structure, about 10 feet (3 meters) thick and 15 feet high to the rampart (the parapet was 5 feet higher). As it was eventually built, the thickness along the wall varied; faces were of dressed stone and the infill of rubble. From Irthing to Bowness a turf-and -timber wall, about 20 feet (6 meters) thick at the base, was initially built and replaced with stone within a few years.
Immediately south of the wall—except in the craggy terrain across the Pennines—there was a continuous ditch (Roman vallum), 10 feet (3 meters) deep and 20 feet wide at the top, with a flat bottom 8 feet (2.4 meters) wide. It was flanked, 30 feet away on each side, by wide earth mounds. These earthworks defined the southern limit of the military zone—in effect, like a customs zone at any modern border.
It was originally intended that the wall would be manned by patrols from small forts called “milecastles” at 600-foot (184-meter, the Roman stadium) intervals. Military and logistical backup would come from established but widely spaced fortresses like Corbridge (Roman Corstopitum), usually at the junction of principal roads. Plans changed during the eight years taken for the building. A total of seventeen forts, some for 1,000 foot soldiers (e.g., Housesteads, Roman Vercovicium) and others for elite, 500-strong cavalry regiments (e.g., Chesters, Roman Aesica), were built at roughly evenly spaced locations along the wall. Each milecastle, serving as a controlled crossing place to the north, had a gate reached by stone causeways across the vallum. Each housed only about two dozen men. Between them, Hadrian’s Wall had two evenly spaced stone observation and signal turrets that were manned by legionaries from the milecastles. Construction was practically complete by a.d. 130, although some work seems to have continued for another eight years. Most of the labor was provided by ordinary soldiers of the three Italian legions then based in Britain, who moved about 1.7 million cubic yards (1.3 million cubic meters) of turf and stone.
The total garrison probably numbered about 12,000, mostly drawn from auxiliary legions raised
in different provinces of the empire. It is clear that such a well-manned outpost was not intended merely for defense; it was used to attack the hostile northern tribes. Moreover, Hadrian’s Wall identified Rome by creating a highly visible boundary. Because traders had to use the milecastles as crossing points to the unconquered territories beyond, and because there was a concentration of population, markets and other social structures developed in some areas. Hadrian was succeeded by Antoninus Pius, who in a.d. 139 commanded another advance into Scotland, reestablishing the frontier. The 37-mile-long (59-kilometer) Antonine Wall was built around a.d. 142 between what is now Old Kilpatrick on the Clyde River and Carriden on the Forth. The 9-foot-high (2.75-meter) turf-faced soil rampart stood on a stone foundation. There was a 40-foot-wide (12-meter) vallum, 12 feet (3.7 meters) deep on its north side. Small forts were located at about 400-yard (370-meter) intervals.
By about a.d. 155 the Romans again retreated from Scotland, to return only briefly between a.d. 159 and 163. Hadrian’s Wall regained its former importance; the vallum, which had been partially filled, was finally reconstructed by about a.d. 208. Breached only three times during the remainder of the occupation—in a.d. 197, 296, and 367—it was retaken on each occasion and rebuilt where necessary to remain the frontier of Roman Britain until the last legions departed in a.d. 410.